1. Field of the Invention:
This invention relates to zoom lenses of simple structure suited to cameras for photography, video cameras, etc. and, more particularly, to zoom lenses of simple structure having three lens units, some of which are moved to effect zooming and which are short in the total lens length and have a good optical performance.
2. Description of the Related Art:
Recently, in the field of lens-shutter cameras and video cameras, minimization of the bulk and size of the camera is advancing. Along this, comes a demand for zoom lenses of smaller size with a shorter total lens length and of simpler form. Of these, the zoom lens whose range includes the standard angle of view (the total angle of view of the field 2.omega.=47.degree. , or, in terms of the 35 mm still camera, about 50 mm in the focal length) and of relatively small size has been proposed in, for example, Japanese Laid-Open Patent Application No. Sho 60-263113.
In this publication, a first lens group, when counted from the object side, of positive refractive power, a second lens group of positive refractive power and a third lens group of negative refractive power, of which the first and third ones are axially moved both forward in a certain condition to vary the focal length from the wide-angle end to the telephoto end, constitute a so-called 3-unit zoom lens of zoom ratio of about 1.5.
In general, with the use of the above-described three lens groups in constructing the zoom lens, to achieve simplification of the construction and arrangement of the constituent lens elements, it is a good idea to reduce the number of lens elements in each lens group to as few as possible.
To admit maintaining the prescribed zoom ratio and the prescribed minimum angle of view of the field, however, the condition in which the lens groups for varying the focal length move relative to each other and the rules of lens design must be set forth appropriate. Otherwise, the range of variation of aberrations with zooming would be caused to increase largely, which raises difficulties in making good correction of these aberrations.